1. Field of the Invention
The present invention relates to a CDMA (Code Division Multiple Access) adaptive antenna reception apparatus, and more particularly to a CDMA adaptive antenna reception apparatus wherein the initial convergence of the antenna weight is completed at a high speed.
2. Description of the Related Art
A conventional CDMA adaptive antenna reception apparatus is disclosed, for example, in N. Nakaminami, T. Ihara, S. Tanaka and M. Sawahashi, “Performance of Coherent Adaptive Antenna Array Diversity Receiver Using the Common Antenna Weights for Rake Combined Paths for W-CDMA Reverse Link”, Technical Report RCS2000-46 of the Society for the Study of the Radio Communications System, the Institute of Electronics, Information and Communication Engineers, June, 2000 or S. Tanaka, Y. Miki and M. Sawahashi, “The Performance of Decision-Directed Coherent Adaptive Diversity in DS-CDMA Reverse Link”, Technical Report RCS96-102 of the Society for the Study of the Radio Communications System, the Institute of Electronics, Information and Communication Engineers, November, 1996.
The conventional CDMA adaptive antenna reception apparatus performs weighted synthesis of signals received by a plurality of antennae by adaptive control to form an optimum beam pattern which has a high directivity in an incoming direction of a desired signal and has the null of a low directivity in an incoming direction of an interference signal. The direction in which the beam pattern has a high directivity is hereinafter referred to as beam direction whereas the direction in which the beam pattern has a low directivity is hereinafter referred to as null direction.
Through the use of such a beam pattern as just described, the conventional CDMA adaptive antenna reception apparatus removes interference from a reception signal and thereby achieves an optimum reception characteristic.
FIG. 5 is a block diagram showing a configuration of a conventional CDMA adaptive antenna reception apparatus. Referring to FIG. 5, the conventional CDMA adaptive antenna reception apparatus includes K (K is an integer equal to or greater than 2) antennae 1-1 to 1-K and a number of adaptive antenna reception sections 102-1 to 102-N equal the number N (N is an integer equal to or greater than 1) of users.
The K antennae 1-1 to 1-K are disposed closely to one another so that they may have a high correlation to one another. A signal from a certain user is received by the antennae 1-1 to 1-K with phase differences caused by path differences which rely upon a relationship between incoming directions of the signal and the antenna arrangement. The antennae 1-1 to 1-K receive signals synthesized from signals from a plurality of users and interference signals such as multi-path interference signals and output the received signals to the adaptive antenna reception sections 102-1 to 102-N.
The adaptive antenna reception sections 102-1 to 102-N all have a same configuration and are allocated to the N users, that is, the first to Nth users. In other words, the CDMA adaptive antenna reception apparatus is capable of processing signals from N users simultaneously. The adaptive antenna reception sections 102-1 to 102-N process the reception signals from the users and individually output discrimination results thereof.
FIG. 6 is a block diagram showing a configuration of an adaptive antenna reception section 102-n (1≦n≦N, n is an integer) of the conventional adaptive antenna reception apparatus. It is to be noted that the number of multi-paths is L (L is an integer equal to or greater than 1).
The adaptive antenna reception section 102-n includes K despreading sections 4-1 to 4-K, L antenna weighting synthesis sections 5-1 to 5-L, an adder 6, K adders 9-1 to 9-K, a further adder 11, a discrimination section 7, a reference signal production section 8 and an antenna weight control section 10.
The antenna weighting synthesis section 5-1 includes K multipliers 5-1-1-1 to 5-1-1-K, a multiplier 5-1-4, K multipliers 5-1-5-1 to 5-1-5-K, an adder 5-1-2 and a channel estimation section 5-1-3. All of the other antenna weighting synthesis sections 5-2 to 5-L have a configuration similar to that of the antenna weighting synthesis section 5-1.
The K despreading sections 4-1 to 4-K are connected to the K antennae 1-1 to 1-K, respectively. The despreading sections 4-1 to 4-K despread signals from the antennae 1-1 to 1-K, respectively, with a spread code allocated to the nth user to separate first path signals and output the first path signals to the L antenna weighting synthesis sections 5-1 to 5-L. The first path signals individually separated by the despreading sections 4-1 to 4-K are inputted to all of the antenna weighting synthesis sections 5-1 to 5-L.
Since the antenna weighting synthesis sections 5-1 to 5-L all have a same configuration, description is given of the antenna weighting synthesis section 5-1.
The K multipliers 5-1-1-1 to 5-1-1-K multiply the outputs of the K despreading sections 4-1 to 4-K by antenna weights outputted from the antenna weight control section 10.
The adder 5-1-2 adds outputs of the multipliers 5-1-1-1 to 5-1-1-K.
The channel estimation section 5-1-3 estimates a channel distortion from an output of the adder 5-1-2 and outputs a complex conjugate of the channel distortion to the multiplier 5-1-4 and the multipliers 5-1-5-1 to 5-1-5-K.
The multiplier 5-1-4 multiplies the output of the adder 5-1-2 and the output of the channel estimation section 5-1-3 and outputs a result of the multiplication as a demodulation signal of the first path.
The K multipliers 5-1-5-1 to 5-1-5-K are connected to the K despreading sections 4-1 to 4-K, respectively. The multipliers 5-1-5-1 to 5-1-5-K multiply the outputs of the despreading sections 4-1 to 4-K by the complex conjugate of the channel distortion outputted from the channel estimation section 5-1-3.
The antenna weighting synthesis sections 5-2 to 5-L output demodulation signals of the second to Lth paths, respectively, similarly to the antenna weighting synthesis section 5-1.
The adder 6 adds the demodulation signals of the first to Lth paths outputted from the L antenna weighting synthesis sections 5-1 to 5-L to perform RAKE synthesis.
The discrimination section 7 performs data discrimination of the signal obtained by the RAKE synthesis of the adder 6 and outputs a result of the discrimination.
The reference signal production section 8 produces a reference signal using the result of the discrimination outputted from the discrimination section 7.
The adder 11 determines an error signal between the signal obtained by the RAKE synthesis of the adder 6 and the reference signal produced by the reference signal production section 8 and outputs the error signal to the antenna weight control section 10.
The K adders 9-1 to 9-K correspond to the K antennae 1-1 to 1-K, respectively.
The adder 9-1 synthesizes the first to Lth path signals separated by the despreading section 4-1 and multiplied by complex conjugates of channel distortions by the antenna weighting synthesis sections 5-1 to 5-L and outputs a despread and path synthesis signal to the antenna weight control section 10.
The adders 9-2 to 9-K synthesize first to Lth path signals separated by the corresponding despreading sections 4-2 to 4-K and multiplied by complex conjugates of channel distortions by the antenna weighting synthesis sections 5-1 to 5-L and output despread and path synthesis signals to the antenna weight control section 10.
The antenna weight control section 110 determines antenna weights controlled to minimize the error signal determined by the adder 11 from the error signal and the despread and path synthesis signals obtained by the adders 9-1 to 9-K and outputs the antenna weights to the antenna weighting synthesis sections 5-1 to 5-L.
As an example of a control algorithm to be used by the antenna weight control section 110, the LMS (Least-Mean-Square) algorithm is available. According to the LMS algorithm, where the antenna weight of the antenna k (2≦k≦K, k is an integer) at time t is represented by Wk(t), the error signal of the output of the adder 11 is represented by e(t) and the path synthesis signal of the kth antenna which is an output of the adder 9-K is represented by xk(t), the antenna weight is updated in accordance with the following expression (1):Wk(t+1)=Wk(t)+μ·xk(t)·e*(t)  (1)where μ is a constant called step size, and * represents a complex conjugate. While, in the conventional example described here, an antenna weight common to all of the first to Lth paths is used, antenna weights different among different paths may be produced and used.
Operation of the conventional CDMA adaptive antenna reception apparatus is described.
The conventional CDMA adaptive antenna reception apparatus shown in FIGS. 5 and 6 receives, at the K antennae 1-1 to 1-K, signals synthesized from signals from a plurality of users and interference signals with the signals from the users such as multi-path interference signals. Then, the CDMA adaptive antenna reception apparatus despread, at the despreading sections 4-1 to 4-K thereof, the signals received by the antennae 1-1 to 1-K using spread codes individually allocated to the adaptive antenna reception sections 102-1 to 102-N.
Thereafter, the CDMA adaptive antenna reception apparatus performs, at the L antenna weighting synthesis sections 5-1 to 5-L thereof, weighted synthesis of the signals obtained by despreading of the despreading sections 4-1 to 4-K with weights determined for the individual channels and further performs compensation of the synthesized signals for channel distortions. In this instance, the CDMA adaptive antenna reception apparatus performs the weighting with antenna weights controlled by the antenna weight control section 110.
Then, the CDMA adaptive antenna reception apparatus RAKE synthesizes, at the adder 6 thereof, the signals synthesized and compensated for by the antenna weighting synthesis sections 5-1 to 5-L, performs, at the discrimination section 7 thereof, data discrimination of the signal obtained by the RAKE synthesis and outputs a result of the discrimination.
In order that a desired signal can be received from whichever direction the desired signal arrives, initial values for antenna weights of a conventional CDMA adaptive antenna reception apparatus are usually set to values with which beam patterns become non-directive. Therefore, much time is required until an antenna weight converges from its initial value to a value with which a beam pattern of an optimum solution wherein the directivity is directed to the direction of a desired signal and the null is directed to the direction of an interference signal is formed.